U.S. patent number 6,440,494 [Application Number 09/543,175] was granted by the patent office on 2002-08-27 for in-situ source synthesis for metal cvd.
This patent grant is currently assigned to Tokyo Electron Limited. Invention is credited to Chantal Arena-Foster.
United States Patent |
6,440,494 |
Arena-Foster |
August 27, 2002 |
**Please see images for:
( Certificate of Correction ) ** |
In-situ source synthesis for metal CVD
Abstract
An in-situ method for synthesis of a vapor type of copper or
other metal precursor from a solid source of metal in an oxidation
state of 1 or greater The solid source is localized above the wafer
and its temperature is controlled independently from the wafer
temperature. The solid source may be located, for example, in a
showerhead. A metal precursor vapor is produced, and this vapor is
drawn onto the wafer, allowing deposition to occur on the wafer and
a solid thin metal film to form on the wafer. The invention
overcomes the problem of low partial pressure of copper precursors
in copper CVD.
Inventors: |
Arena-Foster; Chantal (Mesa,
AZ) |
Assignee: |
Tokyo Electron Limited (Tokyo,
JP)
|
Family
ID: |
24166895 |
Appl.
No.: |
09/543,175 |
Filed: |
April 5, 2000 |
Current U.S.
Class: |
427/250;
427/253 |
Current CPC
Class: |
C23C
16/18 (20130101); C23C 16/4488 (20130101) |
Current International
Class: |
C23C
16/18 (20060101); C23C 16/448 (20060101); C23C
016/18 (); C23C 016/08 () |
Field of
Search: |
;427/250,252,253 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
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|
|
|
|
|
0-222-241 |
|
May 1987 |
|
EP |
|
0-322-466 |
|
Jul 1989 |
|
EP |
|
0-573-348 |
|
Dec 1993 |
|
EP |
|
0573348 |
|
Dec 1993 |
|
EP |
|
1-308804 |
|
Dec 1989 |
|
JP |
|
WO-99/07924 |
|
Feb 1999 |
|
WO |
|
Other References
Norman, J. A. T. et al., New OMCVD Precursors for Selective Copper
Metallization, J. of Physique IV, Editions de Physique, vol. 1,
Sep. 1, 1991, pp. 271-278, XP-002052419, ISSN: 1155-4339..
|
Primary Examiner: Chen; Bret
Attorney, Agent or Firm: Wood, Herron & Evans, LLP
Claims
What is claimed is:
1. A method for depositing a metal film on a substrate, comprising
the steps of: providing a solid source of a metal in an oxidation
state of 1 or greater in a CVD chamber, the source being positioned
above the substrate; injecting an organic gas into the chamber and
heating the source to a temperature sufficient to react the gas
with the solid metal source to form a vapor organometallic
precursor; directing the vapor organometallic precursor toward the
substrate; and heating the substrate to a temperature sufficient to
decompose the precursor on a surface of the substrate to form a
metal film.
2. The method of claim 1, wherein the source is a copper
halide.
3. The method of claim 1, wherein the source is selected from the
group consisting of copper oxide, copper chloride and combinations
thereof.
4. The method of claim 3, wherein said copper is selected from the
group consisting of copper having a 1+ oxidation state (Cu.sup.1+),
and copper having a 2+ oxidation state (Cu.sup.2+).
5. The method of claim 1, wherein the source is a halide or oxide
of a metal selected from the group consisting of: copper,
palladium, nickel, iron, or chromium.
6. The method of claim 1, wherein the chamber includes a showerhead
positioned above the substrate and the source is a plate within the
showerhead.
7. The method of claim 1, wherein the chamber includes a showerhead
positioned above the substrate and the source is a cylinder in the
showerhead.
8. The method of claim 1, wherein the chamber includes a showerhead
positioned above the substrate and the source is a wire in the
showerhead.
9. The method of claim 1, wherein the chamber includes a showerhead
positioned above the substrate and the source is a compressed
powder in the showerhead.
10. The method of claim 1, wherein the chamber includes a
showerhead positioned above the substrate and the source is a
powder in a receptacle in the showcrhead.
11. The method of claim 1, wherein the temperature of the source is
controlled by electrical current flowing in the source.
12. The method of claim 1, wherein the source is heated with
thermal assistance.
13. The method of claim 1 wherein the source is heated with
electrical assistance.
14. The method of claim 1, wherein the organic gas comprises a
first compound capable of generating a bidendate ligand.
15. The method of claim 14, wherein the first compound is
acetylacetonate or hexafluoroacetylacetone.
16. The method of claim 1, wherein the organic gas comprises a
second compound capable of generating a Lewis-based ligand.
17. The method of claim 16, wherein the second compound is
trimethylvinylsilane, cyclooctadiene or triethyl phosphine.
18. The method of claim 1, wherein the gas comprises a mixture of a
first compound capable of generating a bidendate ligand and a
second compound capable of generating a Lewis-based ligand.
19. The method of claim 1, wherein the gas comprises a mixture of
hexafluoroacetylacetone and trimethylvinylsilane.
20. The method of claim 1, wherein the source is heated to a
temperature in the range of about 50.degree. C. to about
500.degree. C.
21. The method of claim 1, wherein the source is heated to a
temperature in the range of about 200.degree. C. to about
300.degree. C.
22. The method of claim 1, wherein the substrate is heated to a
temperature in the range of about 100.degree. C. to about
400.degree. C.
23. The method of claim 1, wherein the substrate is heated to a
temperature of about 200.degree. C.
24. A method for depositing a copper film on a substrate,
comprising the steps of: providing a solid source of copper in an
oxidation state of 1 or greater in a CVD chamber, the source being
positioned above the substrate; injecting an organic gas into the
chamber and heating the source to a temperature sufficient to react
the organic gas with the copper to form a copper organovapor
precursor, wherein the gas comprises a mixture of a first compound
capable of generating a bidendate ligand and a second compound
capable of generating a Lewis-based ligand; directing the copper
organovapor precursor toward the substrate; and heating the
substrate to a temperature sufficient to decompose the precursor on
a surface of the substrate to form a copper film.
25. The method of claim 24, wherein the chamber includes a
showerhead positioned above the substrate and the source is a plate
within the showerhead.
26. The method of claim 24, wherein the first compound is
acetylacetone or hexafluoroacetylacetone.
27. The method of claim 24, where in the second compound is
trimethylvinylsilane, cyclooctadiene or triethyl phosphine.
28. The method of claim 24, wherein the gas comprises a mixture of
hexafluoroacetylacetone and trimethylvinylsilane.
29. The method of claim 24, wherein the source is heated to a
temperature in the range of about 50.degree. C. to about
500.degree. C.
30. The method of claim 24, wherein the substrate is heated to a
temperature in the range of about 100.degree. C. to about
400.degree. C.
Description
FIELD OF THE INVENTION
The invention relates generally to methods for chemical vapor
deposition of a metal, particularly copper, onto a substrate.
BACKGROUND
In the formation of integrated circuits (IC), thin films containing
metal and metalloid elements are deposited upon the surface of a
semiconductor substrate or wafer. The films provide conductive and
ohmic contacts in the circuits and between the various devices of
an IC. For example, a thin film of a desired metal might be applied
to the exposed surface of a contact or via in a semiconductor
substrate. The film, passing through the insulative layers of the
substrate, provides plugs of conductive material for the purpose of
making interconnections across the insulating layers.
One well known process for depositing a thin metal film is by
chemical vapor deposition (CVD). In CVD, reactant or deposition gas
precursors are pumped into proximity to a substrate inside a
reaction chamber. The precursors are activated using either thermal
energy or electrical energy, and subsequently undergo chemical
reactions at the surface of the substrate. This results in one or
more reaction by-products, which are deposited on the exposed
substrate or wafer surface to form a film.
Copper CVD reactions are limited mainly by the low partial pressure
of potential copper precursors. In fact, most of the potential
precursors have such a low partial pressure that use of a gas mass
flow controller (MFC) and vapor draw from a liquid precursor in a
vessel is difficult. Instead, direct liquid injection (DLI) of the
liquid copper precursor must be used.
DLI of a copper precursor, however, is undesirable for several
reasons. One reason is that it requires use of two devices: a first
device to form a mist or aerosol of the precursor liquid, and a
second device to transform the mist into a precursor vapor.
Additionally, during this process the stability of the precursor
source is generally a problem; the precursor tends to decompose or
change composition along the path of its liquid injection and
vaporization. Another reason is that control of the deposition rate
is difficult in DLI of the precursor liquid. Also, the DLI device
may clog if precursor deposition occurs in the device itself.
Moreover, a device such as a showerhead, which is supposed to aid
in uniform distribution of precursor at the surface of the wafer or
substrate, might become hot enough to participate in decomposition
of the copper precursor, and the precursor may deposit on the
showerhead. Such an occurrence would make control of precursor
delivery to the wafer even more difficult.
What is needed is a way to generate a copper or other metal
precursor vapor to avoid problems that arise with injecting a
precursor in a liquid state.
SUMMARY OF THE INVENTION
The present invention is directed to a method of generating a metal
precursor, such as copper precursor, used for CVD within the
deposition reactor. This method generates the vapor precursor from
simple elements in-situ, and thus reduces or eliminates the need to
obtain a sufficient partial pressure to deliver the copper or other
metal precursor. The present invention is also directed to a method
of delivering the vapor precursor to the wafer to deposit a thin
film. To this end, and in accordance with the principles of the
present invention, a solid source of a metal in an oxidation state
of 1 or greater is heated in the chamber above the substrate to a
temperature at which the source will react with a gas injected into
the chamber to form a vapor metal precursor. This precursor is
directed toward the substrate, which is heated so as to decompose
the precursor onto the substrate surface.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic cross-sectional view of a reaction chamber in
the practice of the invention;
FIG. 2 is an enlarged view of the encircled area 2 of FIG. 1;
FIG. 3 is an alternative embodiment of the showerhead of FIG.
2;
FIG. 4 is another alternative embodiment of the showerhead of FIG.
2; and
FIG. 5 is yet another alternative embodiment of the showerhead of
FIG. 2.
DETAILED DESCRIPTION
A copper or other metal vapor precursor is generated in-situ in a
CVD chamber without the aforementioned problem of low partial
pressure of the precursor. The present invention forms and uses the
vapor precursor directly above the substrate surface thereby
minimizing travel of the vapor and the resulting pressure drop.
With flow control, the vapor need not travel through the chamber,
so vapor conductive loss is less. By the method of the present
invention, the partial pressure of the formed vapor becomes less of
a limiting factor in the CVD process. The principles of the present
invention may be best understood with reference to the drawings and
illustrative examples.
With reference to FIG. 1, a reactor 45 used for copper deposition
on the surface 28 of a semiconductor substrate 22 by CVD is
illustrated. The reactor 45 includes a reaction chamber 46 which
encloses a processing space 48. In the reaction chamber 46, which
is shown as containing a substrate 22 on a susceptor 20, reactant
gases for CVD are delivered to a processing space 48. A gas
delivery system, such as the system described in U.S. Pat. No.
5,628,829 METHOD AND APPARATUS FOR LOW TEMPERATURE DEPOSITION OF
CVD AND PECVD REACTIONS, which is assigned to the Assignee of the
present invention and is hereby specifically incorporated in its
entirety by reference, provides the proper flow and distribution of
the gases for the CVD process. Generally, gas delivery systems
contain gas-dispersing elements, such as a flat showerhead 50, in
the reaction chamber 46. The showerhead 50 spreads the entering
reactant gases around the processing space 48 of the reaction
chamber 46 to ensure a uniform distribution and flow of the gases
proximate the susceptor 20 and substrate 22. Uniform gas
distribution and flow is desirable for a uniform and efficient
deposition process, a dense plasma, and a uniformly deposited
film.
According to one embodiment of the present invention, the reactor
45 is equipped with a plasma producing apparatus 51 for exposing
the susceptor 20 to a hydrogen/argon plasma either prior or
subsequent to placing of the substrate 22 thereon for processing.
The apparatus 51 to expose the susceptor 20 to the hydrogen/argon
plasma may be the type described in U.S. Pat. No. 5,906,866
entitled PROCESS FOR CHEMICAL VAPOR DEPOSITION FOR TUNGSTEN ONTO A
TITANIUM NITRIDE SUBSTRATE SURFACE, which is assigned to the
Assignee of the present invention and is expressly incorporated
herein in its entirety by reference. The apparatus 51 preferably
includes a radiofrequency (RF) generator 52, capable of generating
450 KHz, which is attached to the showerhead 50.
In the present invention and with reference to FIG. 2, a showerhead
50 apparatus, as is known to one skilled in the art and as
previously described, may be used. The showerhead 50, located above
the wafer 22, has two plates. A top plate 54a is made of copper and
a bottom plate 54b is made of an inert material with respect to the
chemical introduced into the showerhead. For example, 54b may be
made of stainless steel or aluminum. The copper of the top plate
54a of the showerhead 50 serves as the main source for the copper
that is deposited on the surface 28 of the wafer 22. If a metal
other than copper is to be deposited, such as palladium, chromium,
nickel or iron, then top plate 54a is made of that metal to provide
the source metal for deposition. The showerhead 50 is maintained at
a temperature T.sub.SH of about 50.degree. C. to about 500.degree.
C., and preferably at about 200.degree. C. to 300.degree. C.
A gas mixture that has the property of reacting with copper and
forming a volatile copper compound at T.sub.SH is injected at a
site 56, which is the plenum of showerhead 50.
A gas mixture that has the property of reacting with copper and
forming a volatile copper compound at T.sub.SH is injected at a
site 56, which is a site 56, which is a plenum of showerhead 50. A
mixture of an oxidizer gas, a bidendate ligand and a Lewis-based
ligand is the gas injected in the plenum of showerhead 50. The
oxidizer gas may be any of Cl.sub.2, O.sub.2, HCl, SiCl.sub.4 or
H.sub.2 O.sub.2, and is preferably Cl.sub.2. The bidendate ligand
may be a diketonate gas (i.e., hexafluoroacetylacetone) or
acetylacetone (acac), and is preferably Hhfac. The Lewis-based
ligand may be any of trimethylvinylsilane (tmvs), cyclooctadiene
(cod) or triethyl phosphine (TEP.sub.3), and is preferably tmvs.
This mixture of gases react with the copper of the top plate 54a of
the showerhead 50 and forms a volatile copper compound, for
example, Cu(hfac).sub.2 or hfac--Cu--tmvs. The volatile compound
passes through the holes 58 of the showerhead 50 and is directed
above the surface 28 of the wafer 22.
The wafer 22 is positioned on the heated susceptor 20, also
referred to as a hot plate, which is positioned under the bottom
plate 54b of the showerhead 50. The temperature of the wafer 22 is
maintained at T.sub.W, which is in the range of about
100.degree.-400.degree. C., and preferably about 200.degree. C.
T.sub.W is selected to allow the copper precursor to decompose on
the wafer surface 28 and form a solid copper film 60. In this
process, the copper on the top plate 54a of the showerhead 50 is
consumed. Because the method involves metal purification
principles, it should be possible to have a very pure vapor of the
copper precursor with a minimum of the impurities that could be
contained in the solid copper of the top plate 54a of the
showerhead 50.
As an example of one chemical path that may be used in the present
invention to form the vapor copper precursor, solid copper of the
top plate 54a is brought from a zero oxidation state
(Cu.sup.0.sub.solid) to a higher oxidation state (Cu.sup.1+ or
Cu.sup.2+) by an oxidation reaction with a gaseous compound ("A").
"A" is the same as the oxidizer gas described above, namely
Cl.sub.2, O.sub.2, HCl, SiCl.sub.4 or H.sub.2 O.sub.2, and
preferably Cl.sub.2. If "A" is a chloride molecule, copper chloride
in a solid form CuCl.sub.(solid) is formed at T.sub.SH at the
surface of the top copper plate 54a of the showerhead 50. The
oxidation reaction is as follows: ##STR1##
At the same time or thereafter, a second compound ("B") that can
react with the oxidized copper is introduced in the showerhead
plenum 56. "B" can bind to the oxidized copper and form a volatile
compound ("C"). Compound "B" may be any bidendate ligand, such as
Hhfac. Compound "B" may also be a mixture of Hhfac or other
bidendate ligand and another Lewis-based ligand ("L") such as tmvs,
cod, or TEP.sub.3. Where "B" includes Hhfac, compound "C" may be
volatile Cu.sup.1+ (hfac) or a Cu.sup.2+ (hfac)-based molecule. The
reaction is as follows: ##STR2##
The newly generated volatile compound "C" is then drawn through the
holes 58 of the showerhead 50 above the wafer 22. At T.sub.W, two
molecules of Cu.sup.1+ (hfac) (tmvs) react together to generate
copper metal (Cu.sup.0) and by-products according to the following
disproportionation reaction: ##STR3##
For Cu.sup.2+, that is, when copper is oxidized to a higher
oxidation state, a reduction reaction, for instance with hydrogen,
is necessary to generate copper metal (Cu.sup.0). The reduction
reaction is as follows: ##STR4##
Volatile compound "B" may be either drawn away, such as by pumping,
or recycled in the showerhead 50 together with compound "A".
EXAMPLE 1
The solid source for copper can be either pure copper (Cu.sup.0) or
copper in a higher oxidation state, either Cu.sup.1+ or Cu.sup.2+,
such as CuO or Cu.sub.2 O. The shape and state of the solid copper
source in showerhead 50 may be a top plate 54, as shown in FIG. 2;
a cylinder 62, as shown in FIG. 3; a wire 64, as shown in FIG. 4,
or a compressed powder of any shape or a powder 66 in a receptacle
68, as shown in FIG. 5. The cylinder 62 and receptacle 68 may be
secured within the showerhead 50 by an electrically conductive wire
or rod 70.
Heating of the copper source could be thermally assisted, for
example, by thermal convection, or radiation from a heating or
radiative source. Heating of the copper source may also be
electrically assisted. Since copper is a good electrical conductor,
the copper source may be connected to an electrical power generator
and heated by the Joule effect. The temperature could be controlled
through a current flowing in the copper source, as shown in FIGS.
3-5, by connecting wire 64 or wire or rod 70 to the electrical
power generator.
Copper in a solid form in a zero oxidation state (Cu.sup.0) may
react with Cl.sub.2. Copper is thereby oxidized to, for example, a
Cu.sup.1+ Cl compound, which is a solid. The reaction is as
follows:
The resulting Cu.sup.1+ Cl.sub.(solid) then reacts with Hhfac and a
Lewis-based ligand, tmvs. The products are a hfac-Cu.sup.1+ -tmvs
gas and an acid HCl. The reaction is as follows:
The resulting copper-ligand compound decomposes to form solid
copper in a zero oxidation state (Cu.sup.0) and a copper compound
with two hfac and two molecules of tmvs. This disproportionation
reaction is as follows:
EXAMPLE 2
Copper may be in a higher oxidation state than in Example 1, that
is, Cu.sup.2-. Then, two Hhfac molecules react with Cu.sup.2+
Cl.sub.2 to form hfac--Cu.sup.2+ --hfac+HCl. A protic solvent is
then necessary to reduce hfac--Cu.sup.2+ +hfac. Two molecules of
the acid Hhfac will be formed as follows:
It should be understood that the embodiments of the present
invention shown and described in the specification are only
preferred embodiments of the inventors who are skilled in the art
and are not limiting in any way. Therefore, various changes,
modifications or alterations to these embodiments may be made or
resorted to without departing from the spirit of the invention and
the scope of the following claims.
* * * * *